For the last couple of months I’ve been using Facebook’s watchman for executing a deployment script when my CD pipeline pushed a file onto the target system. Watchman is a bit weird when it comes to running it as a service, though, so I started looking around thinking that this should be something that Systemd should be able to handle all by itself. And to actually nobody’s surprise I found the feature I was looking for: systemd.path.
Similar to a timer you can tell Systemd to activate a service if something happens to a file-system path. A sample setup would look like this:
$cat /etc/systemd/system/app-update.service
[Unit]
Description=app-update executor
After=network.target
[Service]
Type=oneshot
ExecStart=/srv/app/scripts/update.sh
$ cat /etc/systemd/system/app-update.path
[Path]
PathModified=/srv/app/etc/main.yml
[Install]
WantedBy=multi-user.target
Here /srv/app/scripts/update.sh is triggered when /srv/app/etc/main.yml is
modified. If you don’t want to trigger the service whenever the file is
modified but only when the file descriptor is closed again after a
modification, use PathChanged instead.
Just make sure to enable and start the path file when you’re done. Otherwise nothing will happen when the file changes 😅
$ systemctl enable app-update.path
$ systemctl start app-update.path
Do you want to give me feedback about this article in private? Please send it to comments@zerokspot.com.
Alternatively, this website also supports Webmentions. If you write a post on a blog that supports this technique, I should get notified about your link 🙂